About 20 percent of U. S. workers have to work night shifts, resulting in serious consequences such as insomnia, fatigue, reduced alertness, impaired performance, gastrointestinal disturbances, and reduced job and public safety. These problems occur because the circadian clocks of the workers do not usually phase shift (reset) to adjust to the night work, day sleep schedule. Therefore, workers are forced to work during the "wrong" phase of their circadian rhythms, when they are the most sleepy, inefficient, and prone to accidents, and to try to sleep during the day, again during the "wrong" phase, which results in disrupted, shortened sleep and chronic sleep deprivation. We propose to test interventions which are designed to phase delay the circadian clock (set it later) so that circadian rhythms have a more appropriate phase relationship to night work and daytime sleep. These interventions will be tested in a simulated night shift protocol using a schedule which is common in nursing and industry (5 consecutive 8-hr night shifts). The interventions will be: 1) a very dark bedroom and a fixed 7-hr dark time for sleep at home after each night shift, 2) wearing dark goggles on the way home after night work, 3) taking melatonin at bedtime before daytime sleep and 4) intermittent bright light during the night shift. The interventions have been designed to take minimal effort by the subjects, so that they would be feasible for real shift workers, yet be strong enough to significantly improve night work performance and daytime sleep. Several combinations of these 4 interventions will be tested. The outcome measures will be: 1) circadian phase (from the circadian rhythm of endogenous melatonin secretion), 2) daytime sleep duration (from wrist activity monitors and sleep logs) and 3) night work sleepiness and performance (evaluated with a computer administered test battery). The goal is to advise shift workers and their employers about the relative benefits of the various combinations of interventions.